Imagine a support project, where lot of unplanned work is done, in fact unplanned work > planned work . How do you manage this scenario? Definitely scrum, fails to handle this efficiently, because this impacts velocity and team starts deviating from actual strategic work. Kanban does some magic here!! But wait! unplanned ! = expedite. Having an explicit expedite swimlane and moving every unplanned work in their, and getting it done is not Kanban way of handling unplanned work. As a matter of fact, the arrival rate of expedite tickets was reduced to five per year for a company of 1300 employees, including over 100 in the IT department in XIT case study mentioned in blue book. Simple theory is, if there is no urgency, no value of doing it, teams use common sense and convince client and not do it. This is simple use of agile value courage!! But if it adds value and is priority we need to figure out way of doing it, one of which is allocating contingency hours.When the team plans their backlogs, they should use only the planned-work capacity to select the user stories.And use contingency hours for unplanned work. This contingency hours should be adjusted as we move ahead basis historic data. Successful Kanban implementation is one where this contingency/unplanned work finally becomes planned. Chart of Unplanned Time, Plannable Time and Corporate Overhead in a Sprint Some examples of allocating contingency hours in case you don't have any historic data to calculate this, we can use one person per week per sprint or designate certain days like only Wednesday we shall do unplanned work. This is very natural way of handling contingencies, it doesn't impose any overhead on teams, maintaining there constant pace while still gives some structure. To summarize this ultimate goal is improvement, and removing as much ad hoc activities as possible.